Most of us living in the 21st century have complex lives, multiples pressures and demands on time. This is especially true of our careers, with portfolio careers becoming the norm rather than the exception.
Medics in particular have a propensity to attract work, consultants working 14 PAs i.e. 7 days a week are routine, and a part time GP is seldom inactive, so the question arises- "is my jam spread too thin?"
To answer the question you must first understand the question.
In an industrial sense, based on time and process any failure to deliver or be present would suggest inadequate performance. However, the question is a judgement based on jam, and not an industrial metric at all.
Assume your customers ( employers, service users, co- workers, staff) were to respond on your behalf. Their response would be a judgement, a perception. In the jam analogy it's a matter of taste and perspective, if enough of the bread is covered by a non uniform distribution such that there is never a bite of the bread which contains insufficient jam for the taste of the diner then the answer is a negative.
And there's the rub. It is a matter of taste.